Hazard precedence

Scope

A material not specifically listed in the 172.101 Table that meets the definition of more than one hazard class or division must be classed according to the highest applicable hazard class, as specified in 173.2a.

Regulatory citations

• 49 CFR 172.101 — Purpose and use of hazardous materials table
• 49 CFR 173.124 — Class 4, Divisions 4.1, 4.2 and 4.3- Definitions
• 49 CFR 173.2a — Classification of a material having more than one hazard

Key definitions

• Hazard class: The category of hazard assigned to a hazardous material under the definitional criteria of Part 173 of this subchapter and the provisions of the 172.101 table. A material may meet the defining criteria for more than one hazard class but is assigned to only one hazard class.
• Packing group: A grouping according to the degree of danger presented by hazardous materials. Packing Group I indicates great danger; Packing Group II, medium danger; Packing Group III, minor danger.

Summary of requirements

The following materials, which have unique properties, are addressed individually in 173.2a(c):

• Class 1 (explosive) material
• Division 5.2 (organic peroxide) material
• Division 6.2 (infectious substance) material
• Division 4.1 (wetted explosive)
• Limited quantities of a Class 7 (radioactive material)

1. Class 7 (radioactive materials, other than limited quantities, and shipments of UN3507, Uranium hexafluoride, radioactive material, excepted package).
2. Division 2.3 (poisonous gases).
3. Division 2.1 (flammable gases).
4. Division 2.2 (non-flammable gases).
5. Division 6.1 (poisonous liquids), Packing Group I, poisonous-by-inhalation only.
6. Division 4.2 (a material that meets the definition of a pyrophoric material in 173.124(b)(1)).
7. Division 4.1 (a material that meets the definition of a self-reactive material in 173.124(a)(2)).
8. Class 3 (flammable liquids), Class 8 (corrosive materials), Division 4.1 (flammable solids), Division 4.2 (spontaneously combustible materials), Division 4.3 (dangerous when wet materials), Division 5.1 (oxidizers), or Division 6.1 (poisonous liquids or solids other than Packing Group I, poisonous-by-inhalation). Note: The hazard class and packing group for a material meeting more than one of these hazards shall be determined using the Precedence of Hazard Table found in 173.2 (a).
9. Combustible liquids.
10. Class 9 (miscellaneous hazardous materials).